1. The Field of the Invention
The present invention relates to Fiberglass ladders and to their methods of manufacture. More specifically, the present invention relates to an improved fiberglass extension ladder and methods of fabrication of fiberglass ladders which may be extended in length for utilization at various heights.
2. The Relevant Technology
Ladders are commonly used for a variety of applications and are of two general types; 1) straight extension ladders, and 2) folding ladders, commonly called stepladders, which are self supporting. Extension ladders are typically used where they may be leaned against a structure for support. Such ladders usually include an extensible segment that can be used to telescopically extend the length of the ladder as desired. Straight extension ladders are well-known in the art. Typically, such ladders are constructed so as to provide a stationary rail section, commonly referred to as a base rail, and a slide rail, commonly referred to as a fly rail.
Straight extension ladders of the prior art typically consist of a pair of channeled side rails joined by a plurality of rungs, commonly referred to as stringers. The channels of a base rail typically face inward toward the stringers. The channels of a fly rail typically face outward and away from the stringers. The two rail sections are so designed as to allow one side of the fly rail channel to slideably overlap and interface with one side of the base rail channel in such a manner as to allow free longitudinal movement of the fly rail with respect to the base rail without allowing the two rails to be easily separated laterally. Extension ladders typically employ a pair of rung lock assemblies to secure the fly rail to the base rail at various heights. A cable and pulley assembly is typically employed to assist in the longitudinal movement of the fly rail.
Extension ladders of the prior art are typically made of aluminum or fiberglass channels and aluminum or fiberglass rungs. Because aluminum ladders are electrically conductive, the regulations of the Occupational Safety and Health Administration (OSHA) state that such ladders should not be utilized near live electrical wiring. For this reason, ladders consisting of non-conductive fiberglass side rails are preferred by those who work around electricity.
The channeled configuration of the side rails is particularly susceptible to twisting or deflection when torsion loads are exerted thereon. In the prior art it has been necessary to "beef up" the walls of the channels in order to reduce this torsion weakness. The increased thickness of the walls of the channels increases the amount of material employed and thereby increases the overall weight of the ladder proportionally.
Another problem with extension ladders of the prior art is the restricted useable rung space created by the overlapping relationship between the base and fly rails This overlapping effect is doubled by virtue of the fact that the two rail sections overlap on both sides of the ladder.
Another inherent problem common to overlapping side rails of extension ladders of the prior art is the side-to-side sloppiness in the overlapping union of the fly and base rails. By nature of the construction techniques employed in the mating of the fly rails to the base rails of a conventional extension ladder, the tolerances are extremely broad. This condition allows for a considerable amount of slop or side-to-side lateral displacement between the two rail sections.
Additionally, the looseness of the union between the fly and base rails of an extension ladder as described above, allows considerable flex in the union resulting in a sagging effect that increases dramatically as the ladder is extended to its maximum length. This sagging tendency also concentrates torsion components of a load vector upon the two end points of the intersection between the fly rail and the base rail. This concentrated torsion load tends to spread the sides of each interfacing channel and, when the load exceeds the torsion properties of the material, the union of the two rails is compromised and the ladder collapses. The sloppy side-to-side tolerances, as described above, add to this torsion displacement.
In an effort to minimize the effects of torsion displacement, as described above, those skilled in the art have added rung braces to one or more ends of the base rail. These braces tie the extended portions of the side rails to the adjoining rungs. However, in most cases, the braces are limited to the bottom of the base rails, as having them within the area of transverse motion between the two rails introduces dangerous cutting surfaces for the hands and fingers of the operator. Again, the only option left to mitigate the torsion weakness in the side rails is to "beef-up" the material, thereby increasing the overall weight of the ladder.
Typically, extension ladders of the prior art require heavy duty hardware at the top of the base rail to align and hold together the union of the base rail to the fly rail and reinforce, to some extent, the area of the union when the ladder is extended. This hardware is bulky, has relatively sharp edges, increases the weight of the ladder, is an obstruction to the user and thereby represents a safety hazard.
In an effort to maximize the useable space between side rails those skilled in the art have developed a means by which the fly rail sections of an extension ladder are placed directly on top of the base rails. This technique is commonly referred to as "stacking." Rails joined together in the "stacked" position rely solely upon end braces or brackets to keep them together. This necessitates the utilization of heavy duty braces or brackets to compensate for the lack of interlocking components of the base and fly rails. Although these ladders extend the useable rung space between the fly rails to equal that of the base rails, the union is typically very loose and the hardware relatively heavier than traditional ladders of channeled side rail construction. Extension ladders typically employ a rope and pulley mechanism to assist in the movement of the fly rail relative to the base rail. The rope is usually fastened around the bottom rung of the fly rail and extended between the fly rail rungs and the base rail rungs to one of the uppermost rungs of the base rail. There a pulley is attached and the rope extended through the pulley. The rope is then left to hang along the back side of the ladder behind the base rail rungs. When the fly rail is elevated beyond the first few rungs the rope reaches the ground below and is subject to mud, snow or other natural debris. If, while the ladder is so extended, the operator attempts to move the ladder, he or she runs the risk of stepping on the exposed rope end. As the ladder is then lifted prior to relocation, the captured rope end may convey a movement of the rope through the pulley and to the fly rail assembly. If the action is sufficient to lift the fly rail enough to disengage the rung lock assembly from its union with the base rail, the fly rail is free to fall downward when the rope end is released from its captured position.
These qualities of the rope and pulley combination render their application a hazard and an inconvenience to the operator of the ladder. Also, that portion of the rope that extends from the bottom fly rail rung to the pulley unrestricted in its downward direction. A foot or other object that catches or pushes against that portion of the rope can cause it to pull against the pulley and, if pulled far enough, could cause the rope to be pulled through the pulley and disengage itself from the said pulley. Again, this condition renders the rope a hazard and inconvenience to the operator of the ladder. In addition to the foregoing hazards a conventional rope and pulley present to the operator, the typical method of fastening the rope to the lower fly rail rung represents a further hazard and inconvenience. Typically, the rope is looped around the rung and tied in a knot. This method extends the rope across the stepping surface, thereby presenting an obstacle to the operator. In addition, the looped rope is free to slide to one side of the attachment rung, thereby presenting an unpredictable obstacle to the operator.
An inherent weakness in both aluminum and fiberglass ladders are their susceptibility to bending, denting or crushing along the exposed sections of the side rails when the ladder is "tipped over" or dropped from its standing position. In an effort to mitigate this weakness, those skilled in the art have "beefed up" the material thickness in the exposed areas. Again, however, this adds to the material weight of the resulting ladder.
Unlike step ladders, extension ladders do not possess wide, flat end caps at the top of the ladder to which paint trays or other attachments may be affixed. Those with extension ladders, therefore, are usually attached to the rungs thereof. Such attachments are generally confined to the area of the rungs between the side rails. This places the attachments directly in front of the user and inhibits the use of the rungs thus employed as either a stepping surface or a place for the user to hold on to. As a result, the accessories present an obstruction to the user and thereby create a safety hazard.